In order to enhance practicability of voice recognition processing, it is important to enhance not only a recognition technique for uttered voice itself, but also a processing technique for environmental noises superposed on the uttered voice. A so-called noise adaptation processing technique for enhancing the resistance property to environmental noises and thus enhancing practicability of voice recognition processing has been hitherto developed, and for example, techniques as disclosed in Patent Document 1 or Non-patent document 1 have been disclosed.
In the former case, distributions of acoustic models (hereinafter merely referred to as “distributions”) are classified by a predetermined number of groups (hereinafter referred to as “clusters”). Specifically, clustering processing is executed so that a plurality of similar distributions are allocated to the same group, and a predetermined number of clusters are generated. Then, model composition processing is executed on the centroid of each cluster.
Therefore, as compared with a generally-known model composition processing, it is impossible to carry out model composition at a higher speed. However, the amount of calculation required for model composition processing on one distribution is large, and for example when it is applied to so-called built-in equipment such as a car navigation device or the like on the assumption that the performance thereof is kept, installation into equipment may be difficult because of restriction in processing time and equipment mount space.
On the other hand, in the latter case, plural noise models for various noise environment categories are prepared in a memory in advance, and a noise model adaptive to a noise environmental category of a voice input signal is selected, whereby the noise adaptation processing corresponding to the noise environment can be performed. However, when the numbers of noise environmental categories and noise models to be prepared in advance are increased, the memory capacity required to store these information is rapidly increased. Therefore, it is difficult to use this voice recognition device as a built-in type voice recognition device which is installed in mobile equipment or in-vehicle mount type equipment.
[Patent Document 1] Japanese Patent Kokai No. 10-161692
[Non-patent Document 1] Papers of lectures of Acoustical Society of Japan (1-8-4; March in 2000) “EXPANSION OF JACOBI ADAPTATION TO NOISE ENVIRONMENTS” (Toshihiko Akae and other three persons)